A semiconductor laser diode device oscillates in a wide wavelength range from infrared to bluish purple by changing a composition and a structure of a semiconductor. However, because long life and satisfactory characteristics cannot be obtained unless the composition includes a compound semiconductor with good crystallinity, a wavelength band in which the semiconductor laser diode device can actually oscillate is limited, and blue and green wavelength bands with satisfactory chromaticity are still under development. Further, with regard to the blue and green wavelength band, there is no probability yet that a semiconductor laser diode device the output power of which is on the order of watts can be obtained, and there is no device that can be suitably applied to a laser display or the like which requires high brightness. Therefore, as a practical measure, a wavelength conversion light source is gathering attention and is under research and development, in which a wavelength of a fundamental emitted from a semiconductor laser diode device is converted through phase matching with a harmonic using a nonlinear optical crystal having a periodic domain inversion structure (hereinafter referred to as a wavelength conversion device).
A conventional wavelength conversion light source is formed of a semiconductor laser diode device having a high reflection film and an antireflection film applied to end faces thereof, respectively, and a polarization maintaining optical fiber having a Bragg grating disposed in a core portion thereof (see, for example, Patent Document 1). Patent Document 1 describes that the high reflection film and the Bragg grating form a resonator, the semiconductor laser oscillates as a stable and single-mode hybrid laser with a narrow line width, and the wavelength of a fundamental of the laser is converted by a wavelength conversion device. Further, there is also a description that it is not important that the semiconductor laser diode device is a laser, and it may be any gain medium. Further, an example in which a polarization maintaining optical fiber is used, or a waveguide is provided to the wavelength conversion device is described.
Patent Document 1; JP 11-509933 A (pages 6 to 12, FIGS. 1 to 3)